WASHINGTON (CNN) -- Secretary of Defense Donald Rumsfeld has become something a lightning rod over the way the Pentagon has handled reports that U.S. soldiers abused Iraqi detainees at Abu Ghraib prison near Baghdad.

President Bush told Rumsfeld on Wednesday that he was "not satisfied" at the way he received information about the allegations, a senior administration official told CNN, and members of Congress are complaining they were not informed of the investigation of the abuses.

At a private Oval Office meeting, Bush complained about learning of the existence of photographs showing Iraqi prisoners being humiliated and degraded from the media, the official said.

"He was not happy, and he let Secretary Rumsfeld know about it," the official said.

Bush also voiced concern that he was not kept up to speed on the scope of the problem -- and how the Pentagon was handling it, the official said.

The Army's investigation of the allegations found that soldiers at Abu Ghraib committed "egregious acts" and "grave breaches of international law."

Six soldiers have been criminally charged in the case and six others have been reprimanded, with two of those relieved of duty, Rumsfeld said at a Pentagon briefing Tuesday.

Investigators interviewed dozens of witnesses and looked at "numerous photos and videos portraying in graphic detail actual detainee abuse" taken by detention facility personnel at the prison. (Full story)

It was the CBS network's broadcast of those photos last week that set off the current controversy.

The question of when Rumsfeld told Bush of the allegations came up at the daily White House briefing Wednesday.

White House press secretary Scott McClellan said he did not know when Rumsfeld informed the president, but he pointed out that U.S. Central Command issued a news release on the investigation January 16.

"It was some time after Secretary Rumsfeld became aware of it," McClellan said, indicating the president was informed of the allegations in a general way, but he didn't learn of the severity of the abuses until last week.

The investigation was completed in mid-March, Gen. Peter Pace, vice chairman of the Joint Chiefs of Staff, said at the Pentagon briefing Tuesday. (Full story)

Rumsfeld goes before the Senate Armed Services Committee for two hours in an open hearing Friday to tell his side of the story. Afterward, he will appear before the full Senate in a closed hearing, said the panel's chairman, Republican Sen. John Warner of Virginia.

Rumsfeld will be accompanied by Gen. Richard Myers, chairman of the Joint Chiefs of Staff, and by a high-ranking official of the Department of the Army, Warner said.

"He's going to be grilled pretty good about what happened, how it happened, and how far up the chain it looks like it went," said Republican Sen. Saxby Chambliss of Georgia, a committee member.

For his part, Rumsfeld says the Pentagon has done everything right.

"This is a serious problem, and it's something the department is addressing," he told the Pentagon briefing Tuesday. "The system works. The system works."

But at his meeting with Bush, Rumsfeld also made clear that he also felt "he didn't know some things he should have," according to the senior administration official, along with another official.

In appearances on two morning news shows Wednesday, Rumsfeld made no apologies for his handling of the scandal, and stopped short of issuing a full apology to the Iraqi people.

"Any American who sees the photographs that we've seen has to feel apologetic to the Iraqi people who were abused," he said on ABC's "Good Morning America."

Rumsfeld is equally reserved in characterizing how the abuse reports might have damaged the chances for U.S. success in Iraq.

"It is clearly, you know, unhelpful in a fundamental way. It's harmful," he told the Tuesday briefing.

At least one senator, Joseph Biden of Delaware, the ranking Democrat on the Foreign Relations Committee, has suggested that if Congress doesn't get satisfactory answers from senior Pentagon officials, "resignations should be sought" -- including Rumsfeld's.

"You know there's this tradition in the United States Navy that if a captain of a ship goes up on the shoals, almost regardless of whether it's his fault or not, he loses command," Biden said Wednesday on CNN. Rumsfeld is a former Navy pilot.